Preparation of lead-sodium alloys



Patented ManlO, 1942 UNITED 2,276,031 Panama-non or LEAD-SODIUM annoys Harry H. Fisher, Baton Rouge, 1a., and Alfred E. Parmelee and Joseph L. Stecher, Wilmington, Del., assig'nors to E. I. du' Pont de Nemonrs I g I & Company, Wilmington, 13:21., a corporation of Delaware No Drawing.

Application June Serial No. 391,936

12 Claims. (01. 75-167) facture of tetra alkyl lead compounds, is an alloy of lead and sodium, usually an alloy consisting of 90% lead and sodium by weight which is designated by the formula NaPb and is known as lead mono-sodium alloy. In order that satisfactory yields of tetra alkyl lead compounds may be obtained, it is essential that the sodium content of the alloy be accurately controlled within narrow limits. Also, in order to meet production demands, it is necessary that the alloy be produced rapidly and easily with a minimum of operating difliculties.

Several methods have been proposed for preparing lead mono-sodium alloy, but all of them have given considerable difliculty in large scale commercial processes, where quantities of alloy, on the order of 100,000 pounds, are preparedin a single batch. The reaction producing the alloy is exothermic and there is a tendency for sodium to be distilled off if temperatures above 425 C.

are attained. vEven a very slight loss of sodium is deleterious to the product and the subsequent process of preparing tetra alkyl lead compounds. Also, some of thelead-sodium alloys, containing amounts of sodium'greater than 10%, have high freezing points. For example, Na4Pb has a freezinz point of 386 C., NasPbz has a freezing point The most commonly employed process comprised the addition of molten lead to the molten sodium. Good mixing of the ingredients'was obtained by this method, but the contents of the pot would solidify occasionally due to the I formation of high freezing alloys and localized cooling. This process required careful control of the temperature of the reaction mass within 7 very narrow limits since, if the temperature fell of 400 C. and NazPb has a freezing point of 396 0., whereas, NaPb has a freezing point of only 367 C. In the processes, which have been employed heretofore, there has been a tendency for the formation of the higher melting alloys below 400 C., even in a few localized spots, solidification would begin and lost time would result. On the other hand, the temperature had tobe maintained below 425 C. to avoid the danger;

of the loss of sodium. Furthermore, suitable cooling media which are able to withstand the higher temperatures without decomposition are rare and expensive. Thus, the method required careful control and close supervision and, in. Q solidification ocspite of this, total ,or partial curred very frequently. 1

It has also been proposed to add molten lead to the pot and then add sodium to it at a controlled rate. This process had the advantage of avoiding the formation of high freezing mixthe very great disadvantage, inthat, it is verydifiicult to distribute the lighter sodium down into the very much heavier lead mass. Such process required long continued agitation in order to obtain a complete mixing of the ingredients and the production of alloy of uniform quality and hence was objectionable for rapid production on the large commercial scale.

It is an object of the present invention to provide an improved process for the preparation of lead-sodium alloys. Another object of this invention is to provide an improved process for the commercial manufacture of lead monosodium alloy, particularly on'the large scale. Other objects are to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accomplished in accordance with our invention which comprises preparing lead-sodium alloy by melting the lead and sodium separately, adding from about 15% to about %.of the molten lead to a suitable reaction vessel provided with means for agitating the ingredients'and means for transferring heat to and from the ingredients, then gradually adding the molten sodium and the rest of the molten lead simultaneously in the proportion of from about 7.65 to about 3.6 parts of lead for each part of the sodium and at such rate that the temperature of the reaction mass is maintained between 367 C. and about 425 C., while agitating the mass to insure thorough mixture of the ingredients, and, when all the ingredients have been added, continuing the agitation until the formation of the alloy is completed. We have found that, by operating in this manner, we are able to easily and rapidly produce the desired lead-sodium alloy on the large commercial scale without any tendency for solidification, local or otherwise, and apparently without the production of high freezing alloys.

Suitable apparatus for carrying out the process is that disclosed and claimed in Patent 2,043,224 to Amick, Lawrence and Stecher, employing diphenyl compounds as is also disclosed in such patent.

This process is particularly applicable to the preparation of lead mono-sodium alloy. In pre paring such alloy, 9 parts of lead and 1 part of sodium are melted and placed in their respective scale tanks. The initial proportion of lead, from about to about 60%, is then introduced into the alloy manufacturing part and heat is applied to maintain the lead in the molten condition. Agitation of the molten lead is started and the addition of the rest of the lead and the sodium is then started simultaneously. The rest of the lead and sodium are added in such proportion that the addition of each will be completed at approximately the same time. When the initial amount of lead added to the pot is 15%, then the remainder of the lead and the sodium will be added in the proportion of 7.65 parts of lead to 1 part of sodium. When of the lead is added initially, then the proportion of lead and sodium added will be about 7.2 parts of lead to 1 part of sodium. When 28% of the leadis added initially, then the proportion of the lead and the sodium added will be 6.5 parts of lead to 1 part of sodium. When of the lead is added initially, then the proportion of lead and sodium subsequently added will be about 5.85

35% or the lead is added initially and we have found that the best results are obtained when about 28% of the lead is added to the pot initially, as we are thereby enabled to add the rest of the lead and the sodium at the maximum rate with the equipment employed. .Other types of equip ment, having different heat transfer characteristics, may operate most efliciently with the initial addition of different proportions of the lead within the range given. The proportion of the lead added initially will also vary to some extent with the efllciency of the means for agitation, the larger amounts of lead requiring the more efilcient means for agitation in order to obtain a proper mixture of the ingredients in the minimum amount of time.

For rapid large scale operation, it is desirable to add the lead and sodium as rapidly as possible. Preferably, the lead and sodium are added at such rate that the heat generated in the reacti n The is more than sufficient to raise the temperature of the mass above 367 C. and particularly above 390 C., and to require cooling to remove heat from the reaction mass and to prevent the temperature from rising to above 425 C. Under.

such circumstances, the application of heat to the reaction vessel is stopped as soon as the addition of lead and sodium is started and a heat transfer medium for cooling the reaction mass is circulated through the jacket of the vessel. .Agitation must be continued throughout the simultaneous addition of the lead and sodium to insure proper mixing and to aid in the distribution and transfer of the heat produced. Preferably, the rate of the simultaneous addition of the lead and sodium and the removal of the heat from the reaction mass is so correlated as to maintain the temperature of the reaction mass at approximately 400 C. and preferably between about 390 C. and about 425 C. With the equipment of Patent 2,043,224 and employing dlphenyl compounds for heat transfer, we have found that the lead and sodium can be added at such rate that from about 0.5 to about 1.25% of the sodium is added per minute. The best results have been obtained when the lead and sodium are added simultaneously at such rate that about 1% of the sodium is added per minute. The simultaneous addition of the lead and sodium may be at a larger rate where the equipment will permit more rapid removal of the heat from the reaction mass. For the most rapid opera tion, it will generally be desirable to remove the heat from the reaction mass as rapidly as the equipment will permit and to control the temperature of the reaction mass by controlling the rate of addition of the lead and sodium.

After all of the lead and sodium have been added to the reaction vessel, it will generally be necessary to continue the agitation for a further period of time until the reaction is complete and the alloy is homogeneous. During such further agitation, it is generally necessary to apply Example 10,000 pounds of sodium and 90,000 pounds of lead are separately melted and pumped to scale tanks from which the rate of addition of each -can be read. The apparatus here used is essentially that described in U. S. Patent No. 2,043,224, "Production of alkylated lead, issued to, Amick, Lawrence and Stecher. Approximately 25,000 pounds of the-molten lead is now run into a pot, the temperature of which is held at about 400 C. Agitation is now begun, and sodium and lead are added at 100 and 650 pounds per minute, re-

6.5/1. After the addition of the lead and sodium is complete, agitation is continued for about one hour. During this period heat must be added to prevent solidification of the mixture, the temperature being held at approximately 385 to 415 C. Samples of the molten alloy are taken during the agitation period, and. if they show the sodium content to be outside of the desired range, further measured additions of lead or sodium are made as may be necessary. After analysis of the charge shows it to be suitable for use, it is pumped to a'casting device for solidification, cooling and grinding, or, if it is not desired to cast the material immediately, it may be placed in a suitable storage pot.

It will be understood that the above example is given for illustrative purposes only and that our invention is not to be limited thereto. It will be readily apparent to those skilled in the art that various modifications may be made in our process without departing from the spirit of our invention. Other equipment, suitable for processes of this type, may be employed. The amount of lead added initially may be widely varied and the-rate of addition of the rest of the lead and the sodium may be widely varied within the ranges hereinbefore given. While it will generally be possible to add the lead and sodium at a substantially constant rate and it is usually desirable to do so when possible, at times it may be necessary to vary the rates of the simultaneous proportion of 9 parts of lead to 1 part of sodium.

Such process has the disadvantage, however, that there is very little material in the pot and very little surface available for effective heat trans fer during the early part of such process. Accordingly, the addition of the materials, during the first part of the process, must b slow and the absence of excess lead, during the addition, increases the tendency and possibility of producing high freezing sodium-lead alloys.\ Because of these disadvantages, such process is not recommended.

From the above disclosure, it will be apparent that, by our process, we have overcome the disadvantages of the processes previously proposed, since the initial addition of part of the lead insures that the freezing point of the mass never rises above 367 C., the freezing point of lead,

mono-sodium alloy, and efllcient heat transfer is obtained. Furthermore, by the initial addition of part of the lead and the addition of the sodium simultaneously with the remaining lead, localized concentration of sodium, to form high freezing compounds is avoided. Furthermore, by this method, particularly by the addition of lead with the sodium, efficient mixing of the ingredients, as they are added, is insured and long continued agitation, after the addition of the ingredients has been completed, is unnecessary. It

dium, removing heat from tion of the alloy is complete.

set provided with means for agitation and means for heat transfer and then gradually addingthe. molten sodium and the rest of the molten lead simultaneously in the proportion of from about 7.65 to about 3.6 parts of lead for each'part of sodium and at such rate that the temperature of the reaction mass is maintained between 367' C. and about 425 C., and mixing the lead and sodium by agitation of the reaction mass during the addition of the sodium and until 2. The method of making lead mono-sodium alloy which comprises melting 9 parts of lead and 1 part of' sodium, adding from about to about 60% of the molten lead to a reaction vessel provided with means for agitation and means for heat transfer and then gradually adding the molten sodium and the rest of the molten lead simultaneously in the proportion of from about 7.65 .to about 3.6 parts of lead for each part of sodium and at such rate that the temperature of the reaction mass is maintained between about 390 C. and about 425 C., and mixing the lead and sodium by agitation of the reaction mass during the addition of the sodium and until the formation of the alloy is complete.

3. The method of making lead mono-sodium alloy which comprises melting 9 parts of lead and 1 part of sodium, adding from about 15% to about 60% of the molten lead to a reaction vessel provided with means for agitation and means for heat transfer and then gradually adding the molten sodium and the rest of the molten lead simultaneously in the proportion of from about 7.65 to about 3.6 parts of lead for each part of sodium, removing heat from the reaction mass during the simultaneous addition of the lead and sodium, correlating the removal of heat and the addition of the lead and sodium so that the temperature of the reaction mass is maintained between about 367 C. and about 425 C., and mixing the lead and sodium by agitation ofthe reaction mass during the addition of the sodium and until theformation of the alloy is complete.

4. The method of making lead mono-sodium alloy which comprises melting 9 parts of lead and 1 part of sodium, adding from about to about of the molten lead to a reaction vessel provided with means for agitation and means for heat transfer and then gradually adding the molten sodium and the rest of the molten lead simultaneously in the proportion of fromabout 7.2 to about 5.85 parts of lead for each part of sothe reaction mass during the simultaneous addition of the lead and sodium, correlating the removal of heat and the will thus be apparent that, by our method, we

have provided a process whereby lead-sodium alloys can be prepared on a commercial scale in a minimum amount of time and with a minimum amount of processing difliculties. We have therealloy which comprises melting 9 parts of lead and addition of the'lead and sodium so that the temperature of the reaction mass i maintained between about 390 C. and about 425 C., and mix.-'

ing the lead and sodium by agitation of the reaction mass during the addition of the sodium and until the formation of the alloy is complete.

.5. The method of making lead mono-sodium alloy which comprises melting '9 parts of lead and 1 part of sodium, adding from about 15% to about 60% of the molten lead to a reaction vessel-provided with means for agitation and means for heat transfer and then gradually addby successfullysolved a serious problem which 1 part of sodium, adding from about 15% to.

about 60% of the molten lead to a reaction vesing the molten sodium and the rest of the molten lead simultaneously in the proportion of from about 7.65 to about 3.6 parts of lead for each part of sodium and at such rate that from about 0.5% to about 1.25% of the sodium is added per minute, removing" heat from the reaction mass during the simultaneous addition of the lead and I the formasodium at such rate that the temperature of the reaction mass is maintained between 367 C. and about 425 C., and mixing the lead and sodium by agitation of the reactionmass during the addition of the sodium and until the formation of the alloy is complete.

6. The method of making lead mono-sodium alloy which comprises melting 9 parts of lead and 1 part of sodium, adding from about to about 60% of the molten lead to a reaction vessel provided with means for agitation and means for heat transfer and then gradually adding the molten sodium and the rest of the molten lead simultaneously in the proportion of from about 7.65 to about 3.6 parts of lead for eachv part of sodiumand at such rate that about 1.0% of the sodium is added per minute, removing heat from the reaction mass during the simultaneous addition of the lead and sodium at such ratethat the temperature of the reaction mass is maintained between 367 C. and about 425 C.,. and mixing the lead and sodium by agitation of the reaction mass during the addition of the sodium and until the formationof the alloy is complete.

7. The method of making lead mono-sodium alloy which comprises melting 9 parts of lead and 1 part of sodium, adding from about simultaneously in the proportion of from about 7.65 to about 3.6 parts of lead for each part of sodium, removing heat from .the reaction mass as rapidly as possible during the simultaneous addition of the lead and sodium, adding the lead and sodium at such rate that the reaction mass is maintained at temperatures of from 367 C. to about 425 C., and-mixingthe lead and sodium by agitation of the reaction mass during the addition of the sodium and untilthe formation of the alloy is complete.

10. The method of making lead mono-sodium Q alloy which comprises-melting 9 parts'of lead and 1 part of sodium, adding from about 15% to about 60% of the molten lead to a reaction vessel provided with means for agitation and means for heat transfer and then gradually adding the molten sodium and the rest of the molten lead simultaneously in the proportion of from about 7.65 to about 3.6 parts of lead for each-part of-sodium, removing heat from the reaction mass as rapidly as possible during the simultaneous addition of the leadand sodium, adding the lead and sodium at such rate that. the reaction mass is maintained at temperatures of from about 390 C. to about 425 C... and mixing the lead and a sodium by agitation of the reaction mass during to about 35% of the molten lead to a reaction vessel provided with means for agitation and means for heat transfer and then gradually adding the molten sodium and the rest of the molten lead simultaneously in the proportion of from about 7.2 to about 5.85 parts of lead for each part of sodium and at such rate that about 1.0% of the sodium is added per minute, removing heat from the reaction mass during the simultaneous 8. The method of making lead mono-sodium. alloy which comprises melting 9 parts of lead lead simultaneously in the proportion of fromabout 7.2 to about 5.85'parts of lead for each part of sodium, removing heat from the reaction mass as rapidly as possible during the simultaneous addition of the lead and sodium, adding the lead and sodium at such rate that the reaction and 1 part of sodium, adding about 28% of the molten lead to a reaction vessel provided with means for agitation and means for heat transfer and then gradually adding the molten sodium and the rest of the molten lead simultaneously in the proportion of about 6.5.parts of lead'for.

each part of sodium and at such rate that about 1.0% of the sodium is added per minute, remov- 9. The-method of making lead mono-sodium alloy which comprises melting 9 parts of lead and 1 part of sodium, adding from about 15% to about of the molten lead to a reaction yes-f .alloy which'comprlses melting 9 parts of lead .and 1 part of-sodium,adding about'28% of the molten lead to a reaction vessel provided with means for agitation and means for heat .transfer and then gradually adding the molten sodium and the rest of the molten lead simultaneously sel provided with means for agitation and means forheat transfer and then gradually adding the molten sodium and the rest of the molten leadin the proportion of about 6.5 parts of lead for each part of sodium, removing heat from the reaction mass as rapidly as possible during the simultaneous addition, of the lead and. sodium, adding the leadand sodium at such rate that the reaction mass is maintained at temperatures of from about 390 C.'to about 425 C., and mixing mass during the addition of the: sodium anduntil the formation of the alloy is complete.

. HARRYQH. mm,

man. 1''... names. JOSEPH L. s'mcimm 

